Surface inspection apparatus

ABSTRACT

A surface inspection apparatus for observing an edge portion of an object to be inspected includes an illumination device that irradiates an illumination light to the edge portion; and an observation device that forms an image of an observation region of the edge portion illuminated with the illumination light. The illumination device emits a first irradiation beam and a second irradiation beam as the illumination light. The first irradiation beam is incident at approximately right angles to the edge portion for compensating brightness of the image and the second irradiation beam is obliquely incident laterally to the observation region of the edge portion for generating a shadow depending on a surface state of the observation region.

This application is a continuation of International Application No.PCT/JP 2007/063317 filed Jul. 3, 2007.

INCORPORATION BY REFERENCE

The disclosures of the following applications are herein incorporated byreference:

Japanese Patent Application No. 2006-184155 filed Jul. 4, 2006International Application No. PCT/JP 2007/063317 filed Jul. 3, 2007

BACKGROUND OF INVENTION

1. Field of the Invention

The present invention relates to a surface inspection apparatus forobserving an edge portion of an object such as, for example, asemiconductor wafer or a glass substrate for a liquid crystal byirradiating a light to the edge portion.

2. Description of Related Art

In Japanese Laid-Open Patent Application No. 2003-139523, there has beenproposed a surface defect inspection apparatus that irradiates adiffused light to an edge portion of a semiconductor wafer such as asilicon wafer, captures an image of the edge portion by using aplurality of CCD cameras, and inspects foreign matter or the like fromthe captured image.

SUMMARY OF THE INVENTION

The conventional surface defect inspection apparatus includes a C-shapedlight source in the form of a letter C that irradiates a diffused lightto the edge portion of a wafer from above, below, and side and three CCDcameras that capture respective images seen from above, below, and side,respectively. One of the three CCD cameras is provided opposite to aperipheral end face of the wafer. The other two CCDs are disposed in aslanted posture against a front surface and a back surface of the edgeportion of the wafer. The dispositions of the light source and the CCDcameras enable the CCD cameras to efficiently receive a mirrorreflection light of the light irradiated by the C-shaped light sourceand reflected by edge portion.

However, it is difficult for the conventional surface defect inspectionapparatus to find defects and fine unevenness that occurred in the edgeportion from the captured image like the surface defect inspectionapparatus that captures from above an image of a wafer that isilluminated substantially right overhead.

A surface inspection apparatus for observing an edge portion of anobject to be inspected according to the present invention includes: anillumination device that irradiates an illumination light to the edgeportion; and an observation device that forms an image of an observationregion of the edge portion illuminated with the illumination light. Theillumination device is configured to emit a first irradiation beam and asecond irradiation beam as the illumination light, the first irradiationbeam being incident at approximately right angles to the edge portionfor compensating brightness of the image and the second irradiation beambeing obliquely incident laterally to the observation region of the edgeportion for generating a shadow depending on a surface state of theobservation region.

The illumination device may be configured so as to irradiate anillumination light having a distribution of light quantity such that alight quantity of the second irradiation beam is greater than a lightquantity of the first irradiation beam. A point at which the lightquantity of the second irradiation beam emitted from the illuminationdevice is a maximum value is positioned outside a predetermined rangedefined in a direction from the observation region to the illuminationdevice.

The illumination device may include a light source, and a light diffuserplate that diffuses a light irradiated from the light source from alight emission surface and irradiates it as the first and the secondirradiation lights. The distribution of light quantity may be set byadjusting a relative positional relationship between the light sourceand the light diffuser plate. Alternatively, the distribution of lightquantity may be set based on optical properties of the light diffuserplate.

The illumination device may include a first light source that generatesthe first irradiation beam and a second light source that generates thesecond irradiation beam.

It is preferred that the surface inspection apparatus further includes amoving mechanism that relatively moves the illumination device withrespect to the object to be inspected.

It is preferred that in the surface inspection apparatus, theobservation device may include an imaging optical system that forms anenlarge image of the observation region, and an image-capturing devicethat captures the enlarged image.

A light source may be used that emits a light having a bright linespectrum as the illumination light. In this case, the image-capturingdevice is a color image-capturing device.

The above-mentioned surface inspection apparatus can inspect the edgeportion of a semiconductor wafer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-section showing a surface inspectionapparatus according to an embodiment of the present invention;

FIG. 2 is an enlarged side view showing the outline of a principal partof the surface inspection apparatus of FIG. 1;

FIG. 3 is a schematic plan view of the surface inspection apparatusaccording to the embodiment;

FIG. 4 is a diagram showing the distribution of light intensity of adiffuser plate;

FIG. 5 is schematic plan view of a surface inspection apparatusaccording to a modification.

DESCRIPTION OF PREFERRED EMBODIMENTS

The surface inspection apparatus according to an embodiment of thepresent invention is described with reference to FIGS. 1 to 4. Thesurface inspection apparatus is an apparatus that performs inspection byobserving a surface of an edge portion of a silicon wafer. FIG. 1 is aschematic side view showing the surface inspection apparatus accordingto the embodiment of the present invention. FIG. 2 is an enlarged sideview showing the outline of a principal part of the surface inspectionapparatus of FIG. 1. FIG. 3 is a top view of the silicon wafer as anobject of inspection and the principal portion of the surface inspectionapparatus. Using an X-Y-Z coordinate system as shown in FIGS. 1 to 3,FIGS. 1 and 2 each indicate an X-Z plane and FIG. 3 indicates an X-Yplane. As shown in FIG. 2, the edge portion 11 of the silicon waferincludes a planar portion 11 c that continues to a slant portion 11 aand an end face portion 11 b.

As shown in FIG. 1, the surface inspection apparatus includes a diffusedillumination device 20, an epi-illumination device 21, a CCD camera 22,an image processing device 23, a display device 24, and an imagingoptical system 29. The diffused illumination device 20 and theepi-illumination device 21 illuminate an edge portion 11 of asemiconductor wafer 10 such as a silicon wafer mounted on a turntable30. The imaging optical system 29 forms an image of the edge portion 11illuminated by the diffused illumination device 20 and theepi-illumination device 21 with an enlarged field of view region. TheCCD camera 22 captures an enlarged image. The image processing device 23processes the captured image signal from the CCD camera 22 to generateimage data for displaying. The display device 24 displays thephotographic image of the CCD camera 22 generated in the imageprocessing device 23.

The diffused illumination device 20 includes a light diffuser plate 25and a fluorescent lamp 26. The illumination light from the fluorescentlamp 26 is incident to the light diffuser plate 25 to emit a diffusedlight from an emission surface thereof. The illumination light emittedfrom the diffused illumination device 20 has a distribution of lightquantity. That is, it has a distribution of light intensity LD along theY axis on the emission surface of the light diffuser plate 25 as shownin FIG. 4. In the present embodiment, the center of the fluorescent lamp26 and the center of the light diffuser plate 25 are out of alignmentone from another. The fluorescent lamp 26 is provided outside a region Wdefined so as to face a field of view region (field of view region ofCCD) DL of the edge portion 11 laterally in the direction fronting thediffused illumination device 20. As a result, there ca be obtainedcharacteristics LD such that the light quantity is distributed along thedirection of the Y axis in the light emission surface of the lightdiffuser plate 25 as shown in FIG. 4.

The diffused light emitted from the light diffuser plate 25 illuminatesthe slant portion 11 a and the end face portion 11 b of the edge portion11. The diffused illumination device 20 is disposed so as to illuminatethe edge portion 11 of one side (surface) of the wafer 10 obliquely fromabove within the X-Z plane shown in FIG. 2. The diffused illuminationdevice 20 is disposed out of alignment below a straight line CL1 thatpasses a center O of the semiconductor wafer 10 in the X-Y plane shownin FIG. 3.

In FIG. 4, a predetermined region centering on a point Pmax at which thelight quantity shows a peak in the direction of the Y axis of the lightdiffuser plate 25 is indicated by LB2W. On the other hand, apredetermined region centering on an intersection point Plow of thelight diffuser plate with the center line CL1 of the wafer is indicatedby LB1W. Assuming that a light incident to the edge portion 11 from thepredetermined region LB1W is a first irradiation beam LB1, the firstirradiation beam LB1 travels approximately in a normal direction to anouter periphery of the edge portion 11. Assuming that a light incidentto the edge portion 11 from the predetermined region LB2W is a secondirradiation beam LB2, the second irradiation beam LB2 is incident in anoblique direction to the outer periphery of the edge portion 11.

Note that the first irradiation beam LB1 contributes to the brightnessof an enlarged image since it is reflected approximately right above atthe slant portion 11 a of the edge portion 11 and incident to anobjective of the imaging optical system 29. In other words, the firstirradiation beam LB1 compensates for the brightness of the enlargedimage. On the other hand, the second irradiation beam LB2 is reflectedin various directions at the slant portion 11 a and does not contributeto the brightness of the enlarged image but compensates for the accuracyof inspection of defects by forming shadows behind various defects asmentioned later.

In this manner, the diffused illumination device 20 illuminates the edgeportion 11 of the wafer 10 by the first irradiation beam LB1 thatilluminates the outer periphery of the wafer 10 from the normaldirection and by the second irradiation beam LB2 that illuminates theouter periphery of the wafer 10 in an oblique direction. Here, assumingthat a plurality of observation points is lined up at predeterminedintervals in the peripheral direction of the observation region DL ofthe edge portion 11 and a plurality of light emission points is lined upat predetermined intervals in the direction of the Y axis on the lightemission surface of the light diffuser plate 25, then a plurality oflines LB2 that connect these points is defined (see FIG. 4). An anglebetween the line LB2 and the traveling direction of the firstirradiation beam LB1 is greater toward the direction of −Y. In otherwords, the angle of the line LB2 increases continuously toward thedirection of −Y. As a result, in the X-Y plane in FIG. 3 and FIG. 4, theedge portion 11 is illuminated from various directions, so thatprotrusions and depressions of various shapes can be inspected withoutfail.

The diffused illumination device 20 can move in the direction of thearrows shown in FIGS. 3 and 4 through a moving mechanism 40. Since thediffused illumination device 20 is moved as a unit, the distributions ofthe light quantity of the second irradiation beam LB2 and the lightquantity of the first irradiation beam LB1 in the observation region canbe adjusted by relatively shifting the distribution of light quantity LDwith respect to the observation region DL. Therefore, the illuminationlight of the diffused illumination device 20 can be controlled such thatfine protrusions and depressions occurring at the slant portion 11 a orthe end face portion 11 b of the edge portion 11 are emphasized byshadows. For example, prior to inspection, an optimal illumination modeis determined by trials and errors.

The illumination light emitted from the fluorescent lamp 26 contains aplurality of-bright line spectra (lights of various wavelengths, forexample, yellow, violet, blue, and so on). Therefore, even when films ofvarious materials are formed on the semiconductor wafer 10, there arebright line spectra that are not absorbed by the films but reflected bythe films. As a result, the bright line spectra interferes with eachother, so that when a plurality of films are stacked on thesemiconductor wafer 10, different colors can be observed depending onthe thicknesses of the films Accordingly, the surface state of thesemiconductor wafer 10 can be observed as divided depending on therespective colors of the films on the wafer 10. On this occasion, theCCD camera 22 is a color CCD camera.

As shown in FIG. 1, epi-illumination device 21 is disposed above theedge portion 11 of the semiconductor wafer 10. The epi-illuminationdevice 21 causes the light from an epi-illumination light source 27 suchas a halogen lamp to be reflected by a half mirror 28 to illuminate theplanar portion 11 c of the edge portion 11 (see FIG. 2) in the main. Theimaging optical system 29 is disposed as shown in FIG. 1 such that anobservation light that has been reflected by the edge portion 11 of thewafer 10 and transmitted through the half mirror 28 is incident to theimaging optical system 29 to form an enlarged image thereof. The CCDcamera 22 is attached to a camera-connecting barrel of the imagingoptical system 29. It captures an enlarged image and outputs an imagesignal.

Then, the operation of the surface inspection apparatus configured asmentioned above is described.

The semiconductor wafer 10 is mounted on the turntable 30 and rotated bythe turntable 30. On this occasion, the planar portion 11 c of the edgeportion 11 is illuminated mainly by the epi-illumination device 21 andthe slant portion 11 a and the end face portion 11 b are illuminatedmainly by the diffused illumination device 20 as shown in FIG. 2. Amongthe reflected lights from the planar portion 11 c, the slant portion 11a, and the end face portion 11 c, the reflected light within the fieldof view region DL shown in FIG. 3 is transmitted through the half mirror28 and is incident to the imaging optical system 29 to form an enlargedimage with desired brightness. The enlarged image formed by the imagingoptical system 29 is captured by the CCD camera 22. The enlarged imagecaptured by the CCD camera 22 is converted into an inspection imagesignal, which is input into the image processing device 23 and undergoesimage processing to form an inspection photographic image of the edgeportion 11. The inspection photographic image is displayed on thedisplay device 24. The CCD camera 22 performs a photographic operationrepeatedly in synchronization with the rotation of the wafer 10 to takean observation image over the whole circumference of the edge portion11. A plurality of frames of the observation images is stored in amemory not shown.

According to the surface inspection apparatus according to theabove-mentioned embodiment, the following advantages are obtained.

(1) The diffused illumination device 20 is configured to emit the firstirradiation beam LB1 that is incident at approximately right angles tothe edge portion laterally in the observation region DL of the edgeportion 11 in order to compensate for the brightness of the enlargedimage and the second irradiation beam LB2 that is incident obliquely tothe edge portion 11 laterally in order to generate a shadow according toa surface state of the edge portion 11 in the observation region DL. Asa result, protrusions and depressions of various shapes present in theslant portion 11 a and the end face portion 11 b can be shaded whilecompensating for the brightness of the enlarged image. Therefore, thecaptured image signals obtained by imaging the slant portion 11 a andthe end face portion 11 b of the edge portion 11 contain pieces ofinformation on various protrusions and depressions, so that the edgeportion of the wafer can be observed with accuracy based on theinspection photographic signals from the CCD camera 22.

(2) The illumination light from the diffused illumination device 20 iscontrolled such that it has a distribution of light quantity LD as shownin FIG. 4 on the light emission surface of the light diffuser plate 25and the light quantity of the second irradiation beam LB2 that isincident obliquely to the observation region DL laterally in the edgeportion 11 is made greater than the light quantity of the firstirradiation beam LB1 that contributes to the brightness of the enlargedimage. As a result, when there are protrusions and depressions due toadhesion of particles or protrusions and depressions due to losses occurin the slant portion 11 a or the end face portion 11 b, shadows of theprotrusions and depressions generated on the opposite side of thediffusion illumination device 20 are sharp and dense and extend to aconsiderable extent particularly by the second irradiation beam LB2.Therefore, the image of protrusions and depressions captured by the CCDcamera 22, image-processed by the image processing device 23, anddisplayed on the display device 24 is displayed as a photographic imageof which even fine protrusions and depressions are easy to find sinceshadows are emphasized to enhance contrast.

(3) The above-mentioned first irradiation beam LB1 is a light that isincident to the semiconductor wafer 10 in an approximately normaldirection to the outer circumference of the semiconductor wafer 10 andreflected thereby upwards to enter the imaging optical system 29. Thesecond irradiation beam LB2 is a light that is incident to the outercircumference of the semiconductor wafer 10 obliquely in anapproximately normal direction and is reflected to the outercircumference of the semiconductor wafer 10 and is reflected in adirection different from that of the imaging optical system 29. As aresult, both a bright-field-like imaging effect and a dark-field-likeimaging effect of the edge portion 11 (the slant portion 11 a, the endface portion 11 b) are obtained, so that not only the shadows ofprotrusions and depressions but also the surface state of the edgeportion 11 can be observed in detail. Therefore, for example, it ispossible to observe the films stacked on the surface and the edgeportion 11 of the semiconductor wafer 10 to find peeling at the edgeportion 11, bubbles in the films, shadow-less deposition of films, andso on.

(4) The fluorescent lamp 26 is used as a light source of the diffusedillumination device 20. The fluorescent lamp 26 emits a light having aplurality of bright line spectra, so that it enables observation of thecolor of the edge portion 11. Since there are among the plurality ofbright line spectra those bright line spectra that are not absorbed bythe film and reflected thereon, the bright lines reflected on the frontsurface and back surface of the film interfere with each other.Therefore, the film seems in a different color depending on thethickness of the film. This enables the observation of a plurality offilms on the semiconductor wafer 10 as separated by color.

The surface inspection apparatus according to the above-mentionedembodiment may be modified as follows.

(1) The illumination mode of the edge portion 11 may be modifiedaccording to any one of (a) to (c) below depending on the defect to beinspected.

-   (a) It may be configured such that the distribution of light    intensity on the light emission surface of the diffuser plate 24 can    be varied.-   (b) It may be configured such that the types of bright line spectra    emitted from the fluorescent lamp 26 can be varied.-   (c) It may be configured such that the duty ratio of source voltage    applied to the fluorescent lamp 26 can be varied.

By achieving variation of the illumination mode as mentioned above asappropriate, that is, by switching the illumination such that the defectto be inspected can be observed without fail, it is possible to inspectthe edge portion 11 under optical illumination conditions.

(2) An epi-illumination device and a CCD camera may be set also on theback side of the semiconductor wafer 10, that is, on the back side ofthe semiconductor wafer 10 in FIG. 1. The diffused illumination device20 can be used for both the front and the back sides but the diffusedillumination device 20 may be set on each of the front and back sides.On this occasion, also the slant portion 11 a that continues to the endface portion 11 b present on the back side of the semiconductor wafer 10is irradiated with the first irradiation beam LB1 and the secondirradiation beam LB2 from the diffused illumination device 20. Theenlarged image in the observation region on the back side of thesemiconductor wafer 10 may be formed by the imaging optical system andcaptured by the CCD camera.

(3) Although the construction in which the light diffuser plate 25 andthe fluorescent lamp 26 are configured in combination with each other asthe diffused illumination device 20, the present invention is notlimited thereto and the diffused illumination device 20 may beconstituted by the light source alone. For example, it may beconstituted by two fluorescent lamps 26. On this occasion, for exampletwo fluorescent lamps 26A and 26B are used as shown in FIG. 5. Thefluorescent lamp 26A is disposed on the straight line L1 that passes thecenter of the semiconductor wafer 10 near the edge portion 11 of thesemiconductor wafer 10 and the fluorescent lamp 26B is disposed at apoint staggered toward a predetermined direction (downward in FIG. 5)parallel to the straight line L1. This enables illumination of the edgeportion 11 with the first irradiation beam LB1 in the normal directionand the second irradiation beam LB2 at a slant with respect thereto. Bysetting the amount of luminescence of the fluorescent lamp 26B greaterthan the amount of luminescence of the fluorescent lamp 26A disposed ona line that passes the center O of the semiconductor wafer 10, the lightquantity of the second irradiation beam LB2 can be set to be greaterthan that of the first irradiation beam LB1.

(4) A solid amplifier-type image sensor, such as CMOS, may be used inplace of the CCD camera 22.

(5) It may be configured such that the distribution of light quantity inthe observation region is varied in the direction of the Y axis bymoving the diffused illumination device 20 in the direction of the Yaxis. The distribution of light intensity along the Y axis on the lightemission surface of the light diffuser plate 25 can be adjusted bymoving the position of the fluorescent lamp 26 with respect to the lightdiffuser plate 25 along the direction of the Y axis.

(6) The light diffuser plate 25 of the diffused illumination device 20may be configured as follows. The center of the light diffuser plate 25is made to substantially coincide with the center of axle of thefluorescent lamp 26. That is, a light having a substantially uniformdistribution of light quantity is input to the light diffuser plate 25from the fluorescent lamp 26. In addition, the optical properties of thelight diffuser plate 25 are set so that the light is emitted from thelight emission surface as the first and the second irradiation lightshaving the distribution of light quantity LD as shown in FIG. 4.

(7) The surface inspection apparatus according to the present inventioncan inspect edge portions of not only semiconductor wafers but alsovarious objects to be inspected in the form of a flat plate. Otherobjects to be inspected include glass plates for a liquid crystaldisplay panel and so on.

In the above description, various embodiments and modifications havebeen explained. However, the present invention should not be limited tothe contents thereof. Other modes conceivable within the technical scopeof the present invention are also included in the scope of the presentinvention.

1. A surface inspection apparatus for observing an edge portion of anobject to be inspected, comprising: an illumination device thatirradiates an illumination light to the edge portion; and an observationdevice that forms an image of an observation region of the edge portionilluminated with the illumination light, wherein the illumination deviceis configured to emit a first irradiation beam and a second irradiationbeam as the illumination light, the first irradiation beam beingincident at approximately right angles to the edge portion forcompensating brightness of the image and the second irradiation beambeing obliquely incident laterally to the observation region of the edgeportion for generating a shadow depending on a surface state of theobservation region.
 2. A surface inspection apparatus according to claim1, wherein a light quantity of the second irradiation beam is greaterthan a light quantity of the first irradiation beam.
 3. A surfaceinspection apparatus according to claim 2, wherein a point at which thelight quantity of the second irradiation beam emitted from theillumination device is a maximum value is positioned outside apredetermined range defined in a direction from the observation regionto the illumination device.
 4. A surface inspection apparatus accordingto claim 2, wherein the illumination device includes a light source, anda light diffuser plate that diffuses a light irradiated from the lightsource from a light emission surface and irradiates the light as thefirst and the second irradiation lights.
 5. A surface inspectionapparatus according to claim 4, wherein the distribution of lightquantity is set based on a relative positional relationship between thelight source and the light diffuser plate.
 6. A surface inspectionapparatus according to claim 4, wherein the distribution of lightquantity is set based on optical properties of the light diffuser plate.7. A surface inspection apparatus according to claim 1, wherein theillumination device includes a first light source that generates thefirst irradiation beam and a second light source that generates thesecond irradiation beam.
 8. A surface inspection apparatus according toclaim 1, further comprising: a moving mechanism that relatively movesthe illumination device with respect to the object to be inspected.
 9. Asurface inspection apparatus according to claim 1, wherein theobservation device includes an imaging optical system that forms anenlarge image of the observation region, and an image-capturing devicethat captures the enlarged image.
 10. A surface inspection apparatusaccording to claim 1, wherein the illumination light has a bright linespectrum.
 11. A surface inspection apparatus according to claim 9,wherein the illumination light has a bright line spectrum and theimage-capturing device is a color image-capturing device.
 12. A surfaceinspection apparatus according to claim 1, wherein the object to beinspected is a semiconductor wafer.